Fifty years after Okinawa's reversion to Japanese rule, the southern island prefecture has become more important for U.S. forces as a strategic foothold, as China and North Korea move to challenge regional stability.

The prospect of U.S. forces' continued stationing in Okinawa due to the changing security environment, however, has frustrated locals who have long chafed at the presence of foreign troops on their soil and an array of associated problems, such as crimes.

In February, amid growing fears of a Chinese invasion of self-ruled Taiwan, the United States released its "Indo-Pacific Strategy," key guidelines on U.S. policy toward China, stating that Washington will "deter military aggression" against "our allies and partners -- including across the Taiwan Strait."

File photo taken on Feb. 15, 2022, shows U.S. Marine Corps Air Station Futenma, adjacent to a crowded residential area of Ginowan in Okinawa Prefecture, southwestern Japan. (Kyodo)

U.S. Marine Corps Commandant Gen. David Berger's Marine reform program, dubbed "Force Design 2030" and originally released in 2020, envisions enabling small units to maneuver between islands where they could set up ad-hoc bases.

Under this proposal, the 3rd Marine Littoral Regiment was formed in Hawaii in March. Two Marine regiments in Okinawa are expected to be transformed into similar littoral regiments.

"For the Marines, who would engage in a battle first, Okinawa's geographical location is extremely significant," said Yuki Tatsumi, a senior fellow and co-director of the East Asia Program at the Stimson Center, a Washington-based think tank.

Okinawa is home to the bulk of U.S. forces in Japan, accounting for 70 percent of the total acreage exclusively used by U.S. military facilities in the country.

All four branches of the U.S. military have personnel in the prefecture. The Marines have in Okinawa their only Expeditionary Force headquarters outside the United States.

Okinawa fell into U.S. hands in the closing months of World War II in 1945 through the Battle of Okinawa, which began in March that year with the landing of U.S. troops on the Kerama Islands, near the main island of Okinawa.

Around 94,000 civilians, about a quarter of Okinawa's population at the time, as well as over 94,000 Japanese soldiers and about 12,500 U.S. troops died in the course of the battle, according to the Okinawa prefectural government.

Okinawa remained under U.S. rule until May 1972, after Japan regained sovereignty in 1952, leaving many Okinawans feeling abandoned by what they often call "the mainland."

Over the more than seven decades since the war, Okinawa has been impacted by major international events, including the Vietnam War, when the U.S. Kadena Air Base was used as a staging ground for U.S. bombers sent for air raids.

U.S. bases on the island were also used to fly sorties in the 1950-1953 Korean War and the 2003 U.S.-led invasion of Iraq.

The island was also affected by the September 2001 terrorist attacks in the United States as shifting military priorities led to efforts to reorganize U.S. forces, including those stationed in Japan.

Kuo Yujen, a professor and expert on Japanese politics and northeast Asian security at Taiwan's National Sun Yat-sen University, said the Marines' Air Station Futenma and the Air Force's Kadena base in Okinawa constitute "a deterrent to China," and a very important one "not only for Japan or for Taiwan, but for the Pacific as a whole."

With the world witnessing Russia's brutal aggression against Ukraine, Kuo says President Vladimir Putin's claims that Russians and Ukrainians form a cultural and historical unity point to the idea of "historical sovereignty" and are "very similar" to what Chinese leaders say about Taiwan.

China considers Taiwan a renegade province that must be reunited with the mainland, by force if necessary.

In the years before Okinawa's reversion, with local residents calling for the prefecture's return to Japanese rule without preconditions, officials in neighboring countries were also working to keep U.S. bases in Okinawa.

In 1967, Chiang Kai-shek, who was leading the government in Taiwan, told then Japanese Prime Minister Eisaku Sato that Japan should not rush to see Okinawa returned.

Chiang's Nationalist Party, or KMT, had relocated to the island in 1949 following its civil war defeat to the Chinese Communist Party. Japan maintained diplomatic ties with Taiwan, formally known as the Republic of China, until 1972.

In 1969, as tensions continued between North and South Korea following the Korean War, then South Korean President Park Chung Hee told a press conference that the fate of military bases should not be decided by just the Japanese or between Japan and the United States.

The military dictator, who had survived a raid by North Korean commandos on the presidential office the previous year, asserted that U.S. bases "are absolutely necessary for the security of not only Japan but also the whole of Asia."

Since the beginning of this year, North Korea has conducted a flurry of missile tests, including the launch of an intercontinental ballistic missile that fell in the Sea of Japan in March.

According to South Korean media, a U.S. military electronic surveillance aircraft took off from Kadena base on March 15 and flew around the Korean Peninsula to detect missile activity.

Yun Duk Min, former head of South Korea's Korea National Diplomatic Academy, says, "The importance of U.S. forces in Okinawa remains the same, or has even increased."

As new threats emerge, people in Okinawa remain frustrated with noise, crimes and accidents linked to the continued presence of U.S. troops. Their hope to see a reduction of U.S. bases remains an uphill battle.

The Marines' Futenma base, which is vital to the force's readiness for rapid deployment, remains in use more than a quarter century after the two countries originally agreed to return its land to Japan owing to the risks posed to the densely populated residential area neighboring it.

The Japanese government is pressing ahead with a project to build Futenma's replacement base within Okinawa, rather than outside the prefecture, despite strong opposition from local people, including Gov. Denny Tamaki.

In January, activists, experts and other locals set up a group to convey their anti-war message to China, Japan and the United States. The group aims to foster public opinion for dispute resolution through dialogue rather than by force.

"There is an imminent threat of (Okinawa) being turned into a battlefield again," Hiroji Yamashiro, a peace activist and co-head of the group, said at a press conference on the group's launch.